1. Field of the invention.
This invention concerns injection molding nozzles and more particularly heated injection molding nozzles of the type adapted to maintain the injection molding material at a high temperature as it flows through the flow passages in the nozzle and mold.
2. Description of prior art
Injection molding nozzles of the type including a surrounding heating coil, have taken essentially two different forms. The first is the so called "full body" form, in which a tip insert protrudes forwardly from the injection nozzle and surrounds a centrally located heat transfer needle in the injection flow passage. The forward end of the insert tip is shaped with a reduced diameter end within which the flow passage converges into an injection port. The reduced diameter end is inserted into a bore in a mold plate defining in part the mold cavity, with the bore extending directly into the mold cavity. The needle and insert tip conduct heat from the heater coil, such as to maintain the molding material at a high temperature molten condition in the passages adjacent the injection port.
The presence of the reduced diameter end on the insert tip in the mold cavity leaves a slight impression on the molded part, which sometimes is objectionable.
Accordingly, "bodyless" injection nozzles have been developed in which a sprue cavity is provided in the mold plate adjacent an injection port also formed in the mold plate. The "bodyless" injection nozzle is positioned adjacent the injection cavity with a needle protruding forwardly into the sprue cavity in order to maintain the molding material in a molten, easily injectable condition. This approach eliminates the impression left by the reduced diameter end of the full body injection nozzle.
While eliminating the impression left by the full body construction, the needle protrudes a significant distance from the main body into the sprue cavity immediately adjacent an injection port.
The exposed position of the end of the needle prevents good heat transfer from being established from the heater coil into the needle and into the mold material. Thus a high temperature and good fluidity of the injected material is not able to be maintained, resulting in difficulties in practicing injection molding using such bodyless design.
Another difficulty is encountered in conventional injection molding nozzles. The mold cavities are defined by mold plates of varying standard thicknesses. The mold plate surface is utilized to locate the injection molding tip within a bore leading into the mold cavity. This is conventionally done by a large diameter rear portion of the injection nozzle main body positioned against the outer surface of the mold plate. This necessitates stocking a relatively large number of differing injection nozzles configurations adapted to a particular mold plate thickness. It would be advantageous if such need for a number of varying injection nozzle configurations could be eliminated.
Accordingly, it is an object of the present invention to provide an injection molding nozzle and method allowing a "bodyless" configuration, eliminating the impression created by a full body construction, while maintaining good heat transfer from the nozzle heater coil into the injected material at the point of injection into the mold cavity.
It is a further object of the present invention to provide such as injection nozzle and method for allowing the use of a standardized configuration adaptable to various mold plate thicknesses.